Climate signals in coral lipids: Temperature-driven variations in lipid distribution and δ13C of fatty acids

Abstract

Corals represent high-resolution modern and geological archives for reconstructing marine environmental shifts. Although the content and distribution of lipids in modern corals are known to be temperature-sensitive, the quantitative relationships between temperature and various lipid compounds have not been systematically investigated to date. Here, we focus on the development and calibration of emerging lipid-based proxies by systematically investigating the temperature sensitivity of the distributions and concentrations of fatty acids (FAs) and sterols in scleractinian corals (Porites lutea and Acropora millepora) from the western coast of Weizhou Island. Corals were grown in controlled aquarium experiments over a temperature range of 16–32 °C for 2 to 13 weeks, yielding lipid distributions and compound-specific carbon isotopic compositions (δ¹³C) of fatty acids that were evaluated in the context of global coral lipid research. Our results reveal that lipids in soft tissue (i.e., the coral host and algal symbionts), exoskeleton (green layer), and endoskeleton (white layer) exhibit differential responses to temperature change, providing a multi-proxy framework for environmental reconstruction. The relative contents of (C_16:1 + C_18:1)/(C_16:0 + C_18:0) show a linear relationship to temperature within the 11–32 °C range, with threshold effects observed for C_16:0, C_18:0 and C_16:1 at ∼26 °C, making these proxies effective at discriminating between cold-water and tropical conditions. Compound-specific carbon isotopic results show positive correlations between temperature and δ¹³C_16:0FA and δ¹³C_18:0FA in soft tissue and exoskeleton, validating their potential as an indicator of coral response to temperature changes over a range of water depths. Additionally, algal-derived sterols show stepwise or linear relationships with temperature variation, reflecting the differential responses of coral-hosted algae to climate change. By providing quantitative calibrations, this study refines the use of coral lipid archives for interpreting deep-time paleoclimate records as well as for assessing the risk posed to coral reef ecosystems by global warming.